Skip to main content

VPC

Networking 101

IP Addresses

Every host or device on a network must be addressable, meaning that they should have something that can be referenced by in order to reach it as a destination under a defined system of addresses. That thing is called IP Addresses and this is how we can address host in a network.

If one computer want to communicate with another computer, then the address can be used the address to reach each other and send information.

The IP address must be unique on its own network.

IPv4 Addresses

IP addresses are made up of two parts. The network address which is to identify the network that the address is part of. Then the part after is used to identify the host within the network.

IPv4 in the old days were divided into five different classes, A through E.

  1. Class A: The first bit is 0 so it includes network address range from 0.0.0.0 to 127.0.0.0 can be used as network ID. 24 bits for host
  2. Class B: The first bit is 1 and second bit is 0 so it includes network address range from 128.0.0.0 to 191.255.0.0. 16 bits for host.
  3. Class C: The two bit is 1 so it includes network address ranges from 192.0.0.0 to 223.255.255.0. 8 bits for host.

So if a company wants a IPv4 address they would go through of first picking a class of address that they want, which dictate how many host they can have in their network. But as you can see it is limited and the size isn't best fit, since the differences between two classes is huge.

Now after you receive a network address from either class, you can further divide the network into smaller network sections and is called subnetting. And by default each network has only one subnet without subnetting, because it contains all  the host addresses defined within. To do subnetting you would basically provide a subnet mask to mask out the subnets that you are looking into.

Netmask is used for identifying the network that the destination IP address falls under, think of the classes, it is for finding out "which network you belong to". Then you would use Subnet mask if you have subnets to find out which subnet you belong to, then finally use the remaining bits to find the actual host.

Example:

You're issued the IP address 10.10.0.0/16, here the Netmask is 255.255.0.0. But if you are going to divide it into say 4 different subnets then you would need a Subnet mask

10.10.0.0/18
10.10.64.0/18
10.10.128.0/18
10.10.192.0/18

The remaining 14 bits will be used to identify each host within each of the subnets.

2^14 * 4 = 2^16. It is still covering all the host that the original big subnet has, but just divided further for ease of management

CIDR

Stands for classles inter-domain routing.

CIDR let you have a variable length of subnet masking, which is much more efficient compared to those classes we say in the previous section.

CIDR consist of two numbers, the network address then the second part is the Netmask indicating how many bits from left to right to mask the network address.

Let’s take an example:

11000000.10101000.01111011.10000100 -- Dest IP address (192.168.123.132)
11111111.11111111.11111111.00000000 -- Subnet mask (255.255.255.0)
192.168.123.132 / 24

As you can see the part highlighted in green is the network address, while the last 8 bits gives the host address. When the package arrives it will arrive in the 192.168.123.0 subnet and then be processed at the destination address of 192.168.123.132.

To know for AWS: It just basically help define the IP ranges that's all.

IP is made up of segments or octets. /32 says that no octet can change for the host, so it only one host address.

/24 means only last octet can change for the host addresses, and so on.

For example: 192.168.0.0 /16 means that the IP ranges from 192.168.0.0 - 192.168.255.255, you can two octets that can change.

Public vs Private IP

Public IP is assigned by IANA organization, and they also establish standard for private IP uses.

Private IP are as follows:

  1. 10.0.0.0 - 10.255.255.255 (10.0.0.0 / 8) This is for big networks
  2. 172.16.0.0 - 172.31.255.255 (172.16.0.0 / 12) This is for AWS default VPC private network range
  3. 192.168.0.0 - 192.168.255.255 (192.168.0.0 / 16) This is for home networks

Then rest of the IP addresses are public.

 

 

 

 

 

 

Back to top